Stabilization of polypropylene



United States The present invention relates to polyolefin compositions and, more particularly, to the stabilization of stereregular polymers of propylene and higher a-olefins against degradation by light.

Highly crystalline, high molecular weight stereoregular polymers of propylene and higher a-olefins are well known. One of the deficiencies of such polymers which must be overcome to enable their use in many applications is poor stability against the deleterious effect of light.

In accordance with the present invention it has been found that the stereoregular polymers of propylene and higher a-olefins can be stabilized very elfectively against the deleterious effects of light by incorporating in such polymers a small amount of a nickel salt of an a-ketoxime having the formula 0 N 0 H wherein R and R are selected from the group consisting of hydrogen, hydrocarbon radicals and heterocyclic radicals composed of carbon, nitrogen and hydrogen, and wherein R and R can together comprise a hydrocarbon radical forming a ring with the carbons depicted in the formula.

Although any stereoregular polymer of a mono-aolefin having at least 3 carbon atoms can be stabilized by means of the invention, the invention is particularly useful in stabilizing stereoregular polymers of monoolefins having from 3 to 6 carbon atoms including, for instance, polypropylene, poly(butene-l), poly(pentene- 1), poly(3-methylbutene-l), and poly(4-methylpentenel).

The nickel salts of rx-ketoxirnes used as additives in accordance with the invention increase the light stability of stereoregular polypropylene and related stereoregular polymers quite markedly. An even further increase in light stability can be achieved, however, by also incorporating a phenolic compound in the polymer. In fact, such outstanding light stability is obtained that it makes these stereoregular polymers useable for many applications requiring prolonged outdoor exposure.

The nickel salts that are used for the stabilization of stereoregular polymers in accordance with the invention have the formula Nli 0 where R and R are as above defined. They can be made by methods known to the art. A convenient method comprises reacting nickelous chloride with the sodium salt of the appropriate oxime in alcohol.

In the previously assigned formula, the permissible R subs-tituents are numerous and varied. Each of R and R can be hydrogen or a hydrocarbon radical or a heterocyclic radical composed of carbon, hydrogen and nitrogen, and, in addition, R and R can together comprise a hydrocarbon radical forming a ring with the carbon atoms depicted in the formula. Typical hydrocarbon radicals that R and R substituents can oomprise are alkyl, aryl, cycloalkyl, aralkyl and alkaryl atent ice - octadecyl, phenyl, cyclohexyl, benzyl, tolyl and similar radicals. Additionally, R and R can each be a heterocyclic radical such as the pyridyl radical. Specific aketoximes from which the nickel salts can be prepared include 1,2-cyclohexadione monoxime, 2,3-butanedione- 2-oxime, 2,3-octanedione-3-oxime, 1-phenyl-1,2-propanedione-Z-oxime, phenylglyoxaldoxime, and pyridyl monoxime.

The invention will be illustrated by the following examples in which parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 In this example s-tereoregular polypropylene having a birefringent melting point of about 168 C. and a reduced specific viscosity of 3.8 (measured on a 0.1% solution of de-cahydronaphthalene at C.) was thoroughly blended with 0.5%, based on the amount of polypropylene, of the nickel salt of 2,3-butanedione-2- oxime. The blend was extruded into molding powder at 210 C. and the molding powder was then pressed into sheets 25 mils thick. Strips cut from these sheets, and 0.5 inch wide, were fastened onto pieces of white cardboard and exposed to outdoor weathering in Miami, Florida, at a 45 angle facing south. In the outdoor exposure, the development of brittleness in each strip was observed by periodically examining the strip and noting the time elapsed vuntil it became brittle, the embrittlement point being the time elapsed until a strip breaks when bent double. Exposure data are as follows:

Table 1 Embrittlement time Control (no stabilizer) lweek. Stabilized polymer 2 months (25,857

Langleys).

EXAMPLE 2 EXAMPLE 3 The nickel salt of 2,3-octanedione-3-oxime was evaluated in the manner of Example 2 in the amount of 0.5% and found to give an embrittlement time several times that of the control sample.

The amount of the nickel salt incorporated in the polymer can be varied from a very small amount up to several percent. More specifically, beneficial results are normally obtained when it is employed in an amount from 0.01% to about 5% by weight of the polymer.

As previously mentioned, one of the preferred, but optional, modifications of the invention comprises incorporating into the polymer a phenolic compound in addition to the nickel salt. The phenolic compound, when used, preferably comprises from 0.01 to 5% by weight of the polymer. Suitable phenolic compounds that are useful in this embodiment include alkyl phenols, bis-phenols, terpene phenols, aralkyl phenols, and polyalkylchromans. Typical alkyl phenols that can be used include di-tert-butyl-p-cresol, o-nonylphenol, o,o-diisopropylphenol, etc. Bisphenols that are useful include 2, 2'-methylene-bis-(5-isopropylphenol), 2,2-methylene-bis- (4 methyl 6 isopropylphenol), 2,2 methylene bis bis-(4-nonylphenol) 2,2'-isopr-opylidene-bis-(4-methyl-6- isopropylphenol), 2,2-isopropylidene-bis-(4-isopropy1phen01), 2,2-isopropylidene-bis-(4-isopropyl-6-methylphenol) 2,2'-isopropylidene-bis- 4-methyl-6-tert-butylphenol) 2,2-isopropylidene-bis-(4 octylphenol) 2,2-isopropylidene-bis-(4-nonylphenol), 2,2-isopropylidene-bis (4-decylphenol), 2,2'-isobutylidene-bis-(4-methyl-6-tertbutylphenol), 2,2'-isobutylidene-bis-(4-nonylphenol), etc.

Polyalkyl chromans that can be employed include 2(2 hydroxyphenyl) 2,4,4,5',6 pentamethylchroman, 4(2' hydroxyphenyl) 2,2,4,5,6 pentamethylchroman, 2(2' hydroxyphenyl) 5',6 diisopropyl 2,4,4 tri methylchroman, 2 (2-hydroXyphenyl) -5 ,6-diisopropy1-2, 4,4,3',8-pentamethylchroman, 2(2-hydroxyphenyl)-5',6- di-tert-butyl-2,4,4trimethylchroman, 4(2'-hydroxyphenyl- 5',6-di-tert-butyl-Z,2,4-trimethylchroman, 2(2-hydroxyphenyl) 5',6 dioctyl 2,4,4 trimethylchroman, 2(2' hydroxyphenyl)-5',6-dinonyl-2,4,4-trimethylchroman, 4, (2' hydroxyphenyl) 5,6 dinonyl 2,2,4 trimethyl chroman, 2( 2-hydroxyphenyl) -5 ,6-didecyl-2,4,4-trimethylchroman, etc.

Terpene phenols useful in this modification are reaction products of a terpene and a phenol as exemplified by 2,6-diisobornyl-p-cresol, 2,4-dimethyl-6-isobornylphe- 1101, and similar products made by condensing phenol or an alkylphenol with a cyclic unsaturated terpene or dihydroterpene, e.g., camphene, carvomenthene, dipentene, u-pinene and the like.

The composition of the invention can also contain 4 one or more additives in addition to those already mentioned. Such other additives include, for instance, pigments, dyes, antacids, fillers, and the like.

What I claim and desire to protect by Letters Patent is: 1. A solid, stereoregular polymer of an a-olefin having from 3 to 6 carbon atoms containing as a light stabilizerv therefor from 0.01% to about 5% by weight of the polymer of a nickel salt of a-ketoxime having the formula ON 0 H wherein R and R are selected from the group consisting of hydrogen, alkyl, aryl, cycloalkyl, aralkyl, alkaryl, pyridyl, and divalent hydrocarbon radicals, R and R when divalent, being joined to form a ring with the carbon atoms depicted in the formula.

2. The composition of claim 1 in which the nickel salt is that of 2,3-butanedione-2-oxime.

3. The composition of claim 1 in which the nickel salt is that of 2,3-octanedione-3 oxime.

4. The composition of claim 1 containing also a small amount of a phenolic compound selected from the group consisting of alkyl phenols, bis-phenols, terpene phenols, aralkyl phenols and polyalkylchromans.

5. The composition of claim 1 in which the polymer is polypropylene.

References Cited in the file of this patent UNITED STATES PATENTS France Ian. 23, 1959 

1. A SOLID, STEREOREGULAR POLYMER OF AN A-OLEFIN HAVING FROM 3 TO 6 CARBON ATOMS CONTAINING AS A LIGHT STABILIZER THEREFOR FROM 0.01% TO ABOUT 5% BY WEIGHT OF THE POLYMER OF A NICKEL SALT OF $-KETOXIME HAVING THE FORMULA 